This invention relates to improved jacking mechanisms for suspending and moving vertically a well pipe or the like. The invention will be described primarily as utiliuzed for lowering a string of casing into a well. U.S. patent application Ser. No. 6/169,718 filed July 17, 1980 by Boyadjieff et al. on "Well Casing Jack Mechanism", and U.S. patent application Ser. No. 6/268,762 filed June 11, 1981 now abandoned by Boyadjieff et al. on "Well Pipe Jack", show devices which are adapted to be mounted in a well drilling rig and act to lower a string of casing or other pipe into the well when the weight of the string exceeds that for which the derrick and related equipment are designed. These devices include two cylinders located at opposite sides of the well string and having pistons which are actuable upwardly and downwardly by fluid pressure to relatively reciprocate two pipe gripping units in a manner progressively jacking the pipe string downwardly. Pressure fluid may be supplied to the cylinders from a power supply unit at a side of the well through flexible hoses leading to the cylinders, and under the control of an operator on the rig floor.